Coil assembly with threaded stem core



Nov. 3, 1964 s. A. ADAMS ETAL 3,155,895

COIL ASSEMBLY WITH THREADED STEM CORE Filed April 20, 1960 2 Sheets-Sheet 1 M m I II I! r lr I14 Stanley A. Adams Dona/d Huber) IN VENTORS BY @waaiiu 1964 s. A. ADAMS ETAL 3,

COIL ASSEMBLY WITH THREADED STEM CORE Filed April 20 1960 2 Sheets-Sheet 2 Fig.9 92 /0a /00 1 Stanley A. Adams /04 Dona/d Hubert INVENTORS 94 98 United States Patent 3,155,895 COIL ASSEMBLY WITH THREADED STEM CDRE Stanley A. Adams, South Haven, and Donald Hubert, Kalamazoo, Mich, assignors to Adams Electronics Inc., Bangor, Mich.

Filed Apr. 20, 1960, Ser. No. 23,545 7 (Ilaims. (Cl. 323-76) The present invention generally relates to an improved and novel coil assembly involving a core threadedly engaged with the interior of a coil form and generally represents improved and novel structural arrangements over that type of device disclosed in co-pending application Serial No. 20,3 62, filed April 6, 1960, now abandoned.

Basically, the present invention deals particularly with high frequency inductance assemblies in the form of transformers employing a winding that is tuned by varying the position of a ferrous core with respect to the windings. Such devices are generally known as IF transformers and generally include a pair of magnetically coupled coils forming a primary and secondary transformer winding together with a tuning capacitor connected in shunt to the coils respectively with the tuning capacitor serving to tune the coils to the desired frequency range.

The primary object of the present invention is to provide a novel structural arrangement for adjustably connecting the core to the coil form for moving the core in relation to the coil form and, of course, the coils disposed thereon.

In recent developments, coil assemblies such as disclosed in the present invention have been reduced greatly in size thus enabling a considerable saving in space which is important in transistorized circuits and especially in certain installations such as aircraft, portable equipment and the like. The present invention renders it possible and practical to rapidly mass produce coil assemblies which are physically very small and overcome a number of the mechanical as well as the electrical problems prevalent in prior analogous coil assemblies.

Briefly, the present invention includes a shielding can having one end closed except for an opening provided therein and with the other end open to receive the components of the coil assembly. A hollow tubular coil form is used to support one or more windings and it is provided with a base at one end. The base is made of a laminate possessing two superposed plates, and if the capacitor is to be used, it is interposed between the plates of the laminate. The central portions of the base plates are unbroken, that is, without any central hole therein thereby leaving a continuous area for reception of the capacitor. Further, the laminate plates are held together, by a number of grommet or hollow rivets near the edges of the base so that the compressive forces between the plates of the base is high at the edges of the base where it is most needed to prevent capacitor leak.

The manner of supporting the core on the coil form is the most important feature of the present invention. The core is cup-shaped in configuration and is provided with an internally disposed stem concentric therewith with the stern being externally threaded. The hollow coil form is provided with radially and inwardly extending ribs which are triangular in cross-section and circurnterentially spaced for receiving the threaded stem whereby the core may be rotated in relation to the coil form and thus caused to move longitudinally in relation to the coil or coils disposed on the coil form in order to properly tune the windings.

The coil form is constructed of plastic and the base thereof is limited in its insertion into the shielding can by inwardly struck protrusions on the shielding can engaging with the upper surface of the base to oppose the clamping action of inwardly folding prongs on the lower end of the can thereby further clamping the laminate 3,155,895 Patented Nov. 3, 1964 forming the capacitor to further prevent capacitor leaks.

Yet another object of the present invention is to provide a coil assembly which is relatively simple in construction, easy to assemble, adapted to mass production, efiective in operation, and generally inexpensive to manufacture.

These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

FIGURE 1 is a perspective view of the coil assembly of the present invention.

FIGURE 2 is a bottom plan view of the construction of FIGURE 1.

FIGURE 3 is a longitudinal, vertical sectional view taken substantially upon a plane passing along section line 33 of FIGURE 1 illustrating further structural details of the coil assembly including the particular construction of the core and its connection with the coil form and relationship to the winding on the coil form;

FIGURE 4 is a transverse, sectional view taken substantially upon a plane passing along section line 4-4 of FIGURE 3 illustrating further structural details of the invention;

FIGURE 5 is a transverse, sectional view taken substantially upon a plane passing along section line 5-5 of FIGURE 3 illustrating further details of the capacitor;

FIGURE 6 is a top plan view of the coil form of the present invention illustrating the orientation of the ribs of the internal surface thereof;

FIGURE 7 is an exploded side elevational view of the core with portions thereof broken away illustrating the manner of assembly of the threaded stem with the core,

FIGURE 8 is an end elevational view of a modified form of core;

FIGURE 9 is a longitudinal, sectional view taken substantially upon a plane passing along section line 99 of FIGURE 8 illustrating further structural details of the modified form of core; and

FIGURE 10 is a perspective view of the threaded stem attached to the core.

Referring now specifically to the drawings, the numeral It generally designates the coil assembly of the present invention and this coil assembly may be employed for any number of diiferent uses including those uses in which a tuned coil assembly is normally employed and any other uses to which the invention may be adapted.

The coil assembly 1% includes a shielding can 12 including a plurality of side walls 14, an upper end Wall 16 and with the lower end thereof being open. The can 12 is preferably square in configuration in order to define corners 18. The shielding can is made of metal or some other conductive material whereas certain other parts of the coil assembly is constructed of insulating material. The end wall 16 of the can 12 is provided with a centrally disposed aperture 2t and opposed side walls 14 of the can 12 is provided with inwardly prO- jecting burrs 22. which are struck inwardly from the material of the shielding can and generally forms conical projections or abutments disposed interiorly of the shielding can.

Disposed Within the shielding can is a coil form generally designated by numeral 24- Which includes a tubular cylindrical member 26 rigid with and unitary with a generally square base 28. The base 23 is provided with a plurality of notches 3% along opposite side edges thereof and the base constitutes a part of a base assembly 32 which is a laminate composed of base 28 and a second plate 34 having notches 36 therein. Both of the plates 34 and base 28 are made of insulation material, for instance plastic, and this is also true of the coil form 24. The base assembly is of such a dimension that it will fit within the shielding can 12 and will substantially fit the open end thereof.

In these forms of the invention where a capacitor is required, a thin fiat capacitor is interposed between the plates 28 and The capacitor is designated by numeral 3 8 and in order to increase capacity, the capacitors 38 could be stacked. However it i preferred that capacitor 38 be made of a mica sheet with conductive coatings 4% on both surfaces thereof. Of course, base sheets other than mica may be selected in order to alter the dielectric strength thereof. For example, barium .titanate or some other earth ceramic may be employed.

The capacitor 38 is provided with notches 42 and 44 in the side edges thereof and are also provided two insulating panels 46 and 48 on opposite surfaces of the capacitor 33. The panels 46 and 48 have apertures which align with the notches 42 and 4 4 and with upper and lower holes b and 52 in plates 28 and 34. This arrangement allows the fasteners or grommets 54 to function as a means for holding the laminated base assembly into a single unit and the fasteners may be either grommets or hollow rivets which are easily applied by machine.

A number of terminal lugs as are employed which have flattened portions 62 at right angles to the shank portions and for a single capacitor 38 to flattened porions 62 are required to make contact. One of the flattened portions 62 is in engagement with one conductive surface dtl of the capacitor 38 while the other flattened portion 62 of another terminal lug 6% is in engagement with the opposite conductor surface 4t) of the capacitor 38. The shanks of the lugs 60 extend through notches 3d and project outwardly beyond the lower open end of the shielding can 12. The capacitor contacting portions 62 of the lugs as are held in firm engagement with the conductor surfaces 4% of the capacitor 33 by compressive forces generated by way of the fasteners 54. Also, the inwardly folding lugs 64 on the lower end of the can 12 serve to further clamp the capacitor 38 between the plates 28 and 34 since this assembly is clamped between the lugs 64 and the inwardly projecting projections or burrs 22.

The positioning of the eyelets or rivets 54 near the edges of the base instead of at the center of the base provides advantages in which the center portions of the plates and 3 are left uninterrupted and the compressive forces are localized adjacent the portions 62 of the lugs dtl. Of course, this is the area in which the highest compressive force is most advantageous for properiy maintaining contact between the capacitor and the lugs even during changes in temperature, humidity and the like which quite often cause poor contacting relation due to dissimilarity in coefl'icient of expansion and the like.

A coil winding 63 is wound on the tubular coil form 26 and is disposed intermediate the ends of the coil form. The extent and length of the coil winding may vary as desired and the leads 7ft from the coil winding es are attached to the lugs 6% by soldering or the like in the region of the notches 30. It will be appreciated that the leads "in occupy a protected position within the coil assembly and extend from the coil winding 68 to the lugs as.

A cup-shaped core 76 is provided which is constructed of a magnetic substance such as compressed powdered ferrite, powdered iron having lower permeability or any suitable equivalent material. The core 76 is provided with a slot or kerf '78 in the upper end thereof for alignment with the opening 26) in the shielding can 12 to provide access to the slot '78 for rotating the core 76 with a suitable instrument. The lower end of the core 7 s is provided with an enlarged recess '79 and the bottom of the recess is designated by 8b and is provided with a recess 82 formed therein. In order to further prevent the core from rubbing against the lead wires coming from the coil, the core '78 is provided with a radiused inner edge thereby forming a smooth rounded surface directed toward the wires '70 around the entire inner circumference of the core 76. Disposed concentrically of the recess 82 and also the recess 76B is a threaded stem 34-. The threaded stem 34 has the inner end thereof disposed within the recess 32 and the outer end thereof generally terminate flush with or even with the bottom edge of the core "76. The external surface of the stem 8 is provided with threads $6 and an epoxy resin or glue 3% is disposed intermediate the threads 86 and the recess 32 so that when the resin or glue 8% hardens, the stem 84 will be rigidly secured to the core '76 and become an integral part therewith.

The tubular coil form as which is constructed of plastic is provided with integral and unitary ribs 9t) which project inwardly into the interior of the coil form and which are of triangular configuration with an equal radial distance and circumferential distance at the base of the triangle. The triangular ribs tl are threadedly engaged with the threaded stern 84 whereby rotation of the core and stem will cause adjustment of the core in relation to the winding.

T e ribs 9d are constructed of a flexible plastic and the engagement of the screw threads 86 with the ribs 90 provides a frictional resistance to rotation of the core 76 thus locking the core in adjusted position in relation to the coil winding 63.

The advantage of using the triangular ribs 90 is that the point or apex of the triangle allows the edge of the thread on stem 86 to engage itself gradually into this stationary rib which does not flex with the rotation of the core in either direction. The base of the triangle or the area approaching the base increases in bodyv or width, this furnishes the engaged core with the ability or strength to withstand more than the usual push strength specifications that are generally applicable in this type of unit. The triangular configuration also pro vides a peak which is readily penetrable by the threads and allows the threads to work into the ribs.

Also, it is pointed out that the leads 7d are protected from engagement by the core inasmuch as the core can progress only so far in one direction inasmuch as the upper surface or end of the coil form 26 will normally engage the core and form a stop for the core before the rounded edges of the core comes into contact with the leads '70.

The stem 84 in the form of the invention illustrated in FIGURES 1-7 is constructed of magnetic material of the same properties as the core '76. In FIGURES 8-10, there is illustrated a modified form of cup-shaped core designated by numeral 92 which includes a centrally disposed stem 94- with a longitudinal polygonal projection :36 received within a complementary socket 98 of similar polygonal shape in the end of stem 1% of flexible plastic material. The stem lltltl is provided with external threads Hi2. thereon for engagement with the ribs 9t? and the stem may be held in position by an epoxy glue or resin 11%. In this form of the invention, the polygonal, for example, square, projection 96 and complementary socket 98 provides a driving coupling between the stem liltiand the stem 94 of the core 92 thus providing for transmittal of torque. The external surface of the core @2 is smooth as indicated by numeral Th2 which is also the situation in the core 78;

The device may be assembled in an obvious manner in which the coil winding, the base and the core are all assembled and then inserted into the shielding can after which the tabs or lugs 64 on the shielding can may be bent over thus enabling the device to be used.

While various dimensions may vary, it is pointed out that the ribs are preferably six in number which are equally spaced circumferentially and each of which is 008 inch wide and .008 inch high and are disposed in a coil forrn having an outside diameter of .147 inch and a wall thickness of .020 inch and the coil form is constructed of a flexible plastic of any suitable type. The threaded stem is provided with a major diameter of .125 inch and a minor diameter of .100 inch. Thus, it will be seen that the minor diameter of the threaded stem is less than the diametrical distance between tips of the ribs 94 but the major diameter is greater than the diametrical distance between the tips of the ribs thus providing resistance to rotation of the core due to the frictional engagement between the threads and ribs caused by the memory characteristics of the flexible plastic. While the ribs are described as being constructed of flexible plastic they, are not in themselves defiectable circumferentially since they are of equilateral triangular configuration.

In that form of the invention employing the plastic stem 1% constructed of the same material as the ribs, the stem projects outwardly beyond the edge of the core 92. The land diameter of the thread 192 is equivalent to the diameter of stem 1%. Thus, the core 92 will be limited in its movement in the same manner as core 7% in that it will engage the end of the coil form.

The epoxy resin for securing the stems in position provides adequate anchorage between the core and the stern and it is noted that in the form of the invention employing the ferrite stem, the lowermost spiral thread forms means for retaining the stem in the epoxy resin.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.

What is claimed as new is as follows:

1. In a coil assembly, a coil form for a winding, a base plate integral with the coil form, a shielding can enclosing said coil form, a cup-shaped core disposed in said can and enclosing the end portion of the coil form remote from the base plate, and a threaded stern rigid with said core and threadedly engaged with the coil form for adjusting the core in relation to the coil form.

2. In a coil assembly, a coil form for a winding including a base plate, a tubular coil form rigid with the base plate, a plurality of radially and inwardly extending ribs disposed inwardly of the tubular coil form, a cup-shaped core enclosing the upper end of the coil form, a winding on the coil form disposed inwardly of the cup-shaped core, and a stern disposed concentrically in the core and having external threads thereon in threaded engagement with the ribs on the coil form for varying the position of the core in relation to the winding on the coil form.

3. The structure as defined in claim 2 wherein said stem is in the form of an externally threaded permeable member having the inner end thereof received within a socket in the bottom of the cup-shaped core, and means bonding the stern in position in the recess in the cupshaped core.

4. In a coil assembly, a coil form for a winding including a base plate, a tubular coil form rigid with the base plate, a plurality of radially and inwardly extending ribs disposed inwardly of the tubular coil form, a cup-shaped core enclosing the upper end of the coil form, a winding on the coil form disposed inwardly of the cup-shaped core, a stern disposed concentrically in the core and having external threads thereon in threaded engagement with the ribs on the coil form for varying the position of the core in relation to the winding on the coil form, said stern including a projection of permeable material having a polygonal end portion, and a threaded stem having a polygonal socket engaged with the projection, means securing the socket onto the projection with the threaded stern thus being rigidly secured to the core, said threaded stem being constructed of plastic materal for engagement with the ribs of the coil form.

5. In a coil assembly, a coil form for a winding, a base having a base plate fixed to the coil form, terminal lugs, means attaching the lugs to said base, a shielding can containing said coil form, a core in said can, means interconnecting the core and the coil form for adjusting the core in relation thereto, said base having a second base plate superposed with respect to the first mentioned base plate, a capacitor between said base plate, portions of said lugs located between said base plates and engaging said capacitor, and a plurality of fasteners spaced from the centers of said plates and engaging both plates and compressively retaining said lug terminal portions engaged between said plates and with said capacitor, said shielding can having inwardly extending projections engaging the top surface of the base plate of the coil form, and inwardly extending tabs engaging the lower surface of the second base plate thereby further compressively retaining the base plate, capacitor and lugs in compressed relationship to prevent capacitor leakage therebetween.

6. In a coil assembly, a coil form for a winding including a base plate, a tubular coil form rigid with the base plate, a plurality of radially and inwardly extending ribs disposed inwardly of the tubular coil form, a cup-shaped core enclosing the upper end of the coil form, a winding on the coil form disposed inwardly of the cupshaped core, and a stem disposed concentrically in the core and having external threads thereon in threaded engagement with the ribs on the coil form for varying the position of the core in relation to the winding on the coil form, each of said ribs being constructed of plastic material and being of equilateral triangular configuration that do not flex with the core in either direction and providing the requisite push through strength.

7. In a coil assembly, a one-piece coil form and base plate therefor including a generally rectangular plate and a cylindrical coil form extending perpendicularly therefrom substantially at the center thereof, the area of said plate disposed outwardly of said coil form being free of obstructions, the periphery of said plate including notch means for receiving wire leads, said plate also including apertures intermediate the coil form and peripheral edge thereof for receiving fasteners, the interior of said coil form having a plurality of inwardly extending longitudinal ribs on the inner surface thereof, said ribs being equally spaced circumferentially and of substantially equilateral triangular configuration for receiving a threaded core stern and retaining such threaded core in adjusted position.

References Cited in the file of this patent UNITED STATES PATENTS 

2. IN A COIL ASSEMBLY, A COIL FORM FOR A WINDING INCLUDING A BASE PLATE, A TUBULAR COIL FORM RIGID WITH THE BASE PLATE, A PLURALITY OF RADIALLY AND INWARDLY EXTENDING RIBS DISPOSED INWARDLY OF THE TUBULAR COIL FORM, A CUP- SHAPED CORE ENCLOSING THE UPPER END OF THE COIL FORM, A WINDING ON THE COIL FORM DISPOSED INWARDLY OF THE CUP-SHAPED CORE, AND A STEM DISPOSED CONCENTRICALLY IN THE CORE AND HAVING EXTERNAL THREADS THEREON IN THREADED ENGAGEMENT WITH THE RIBS ON THE COIL FORM FOR VARYING THE POSITION OF THE CORE IN RELATION TO THE WINDING ON THE COIL FORM. 